The present invention generally pertains to a method of operating microsurgical instruments. More particularly, but not by way of limitation, the present invention pertains to a method of operating microsurgical instruments used in posterior segment ophthalmic surgery, such as vitrectomy probes, so as to optimize the performance of the instruments for a variety of surgical objectives.
Many microsurgical procedures require precision cutting and/or removal of various body tissues. For example, certain ophthalmic surgical procedures require the cutting and/or removal of the vitreous humor, a transparent jelly-like material that fills the posterior segment of the eye. The vitreous humor, or vitreous, is composed of numerous microscopic fibers that are often attached to the retina. Therefore, cutting and removal of the vitreous must be done with great care to avoid traction on the retina, the separation of the retina from the choroid, a retinal tear, or, in the worst case, cutting and removal of the retina itself.
The use of microsurgical cutting probes in posterior segment ophthalmic surgery is well known. Such vitrectomy probes are typically inserted via an incision in the sclera near the pars plana. The surgeon may also insert other microsurgical instruments such as a fiber optic illuminator, an infusion cannula, or an aspiration probe during the posterior segment surgery. The surgeon performs the procedure while viewing the eye under a microscope.
Conventional vitrectomy probes typically include a hollow outer cutting member, a hollow inner cutting member arranged coaxially with and movably disposed within the hollow outer cutting member, and a port extending radially through the outer cutting member near the distal end thereof. Vitreous humor is aspirated into the open port, and the inner member is actuated, closing the port. Upon the closing of the port, cutting surfaces on both the inner and outer cutting members cooperate to cut the vitreous, and the cut vitreous is then aspirated away through the inner cutting member. U.S. Pat. Nos. 4,577,629 (Martinez); 5,019,035 (Missirlian et al.); 4,909,249 (Akkas et al.); 5,176,628 (Charles et al.); 5,047,008 (de Juan et al.); 4,696,298 (Higgins et al.); and 5,733,297 (Wang) all disclose various types of vitrectomy probes, and each of these patents is incorporated herein in its entirety by reference.
Conventional vitrectomy probes include xe2x80x9cguillotine stylexe2x80x9d probes and rotational probes. A guillotine style probe has an inner cutting member that reciprocates along its longitudinal axis. A rotational probe has an inner cutting member that reciprocates around its longitudinal axis. In both types of probes, the inner cutting members are actuated using various methods. For example, the inner cutting member can be moved from the open port position to the closed port position by pneumatic pressure against a piston or diaphragm assembly that overcomes a mechanical spring. Upon removal of the pneumatic pressure, the spring returns the inner cutting member from the closed port position to the open port position. As another example, the inner cutting member can be moved from the open port position to the closed port position using a first source of pneumatic pressure, and then can be moved from the closed port position to the open port position using a second source of pneumatic pressure. As a further example, the inner cutting member can be electromechanically actuated between the open and closed port positions using a conventional rotating electric motor or a solenoid. U.S. Pat. No. 4,577,629 provides an example of a guillotine style, pneumatic piston/mechanical spring actuated probe. U.S. Pat. Nos. 4,909,249 and 5,019,035 disclose guillotine style, pneumatic diaphragm/mechanical spring actuated probes. U.S. Pat. No. 5,176,628 shows a rotational dual pneumatic drive probe.
With each of the above-described conventional vitrectomy probes, the inner cutting member is always actuated from a fully open port position, to a fully closed port position, and back to a fully open port position. It is believed that certain conventional guillotine style, pneumatic/mechanical spring actuated probes are physically capable of being operated at cutting speeds that do not allow the port to return to its fully open position in each cut cycle. However, the surgical systems with which such probes have been operated have not allowed this mode of operation to occur. This is because the ophthalmic surgical community has historically believed that a fully open port is critical to maximize fluid flow into and inclusion of vitreous within the port and to expedite vitreous cutting and removal.
Most conventional probes are sized to have a relatively large fully open port size (e.g. 0.020 inches to 0.030 inches) for use in a variety of surgical objectives. Operating at relatively low cut rates (e.g. up to 800 cuts/minute), these probes may be used to remove large amounts of vitreous in a single cut cycle, such as in core vitrectomy, and to cut physically large vitreous tissue, such as traction bands. In addition, these probes are also used to perform more delicate operations such as mobile tissue management (e.g. removing vitreous near a detached portion of the retina or a retinal tear), vitreous base dissection, and membrane removal. However, the combined effect of large port size, large cut stroke, and relatively slow cut rate of these probes sometimes creates unwanted turbulence of the vitreous and retinal tissues and a large peak to peak fluctuation of intraocular pressure within the eye. Both of these limitations cause difficulty for the surgeon and can be detrimental to the patient.
Specialized vitrectomy probes have been developed. For example, probes with relatively smaller fully open port sizes (e.g. 0.010 inches) have been used to perform more delicate surgical objectives near the retina. An example of such a specialized probe is the Microport(copyright) probe available from Alcon Laboratories, Inc. of Fort Worth, Tex. However, these probes are not highly effective for core vitrectomy, and thus the surgeon is often forced to use and repeatedly insert multiple vitrectomy probes within a patient""s eye, complicating the surgery and increasing trauma to the patient. As another example, U.S. Pat. Nos. 4,909,249 and 5,019,035 disclose probes with manually adjustable port sizes. However, repeated manual adjustment of port size is time consuming and awkward. Relatively high cut rate probes have been developed by Storz Instrument Company of St. Louis (the xe2x80x9cLightningxe2x80x9d probe) and Scieran Technologies, Inc. of Laguna Hills, Calif. (the xe2x80x9cVit Commanderxe2x80x9d probe). However, it is believed that these probes are somewhat limited in flow rate, rendering them less effective for core vitrectomy.
Therefore, a need exists for an improved method of performing all of the fundamental aspects of vitrectomy surgeryxe2x80x94core vitrectomy, mobile tissue management, vitreous base dissection, and membrane removalxe2x80x94that does not suffer from the above-described limitations. As is explained in greater detail hereinbelow, this method would automatically control cut rate, port open duty cycle, and port open size or aperture as needed during a procedure to achieve a broad range of surgical objectives. An improved method is also needed for operating microsurgical instruments other than vitrectomy probes. Ideally, the improved methods would be safe for the patient, easy for the surgeon to use, and economically feasible.
One aspect of the present invention comprises a method of operating a microsurgical instrument. The microsurgical instrument includes a port for receiving tissue and a member. A flow of tissue is induced into the port with a vacuum source, and the member is actuated in a cyclic manner to open and close the port over a plurality of cycle rates. A duty cycle of the member is varied with the cycle rate to vary the flow of the tissue into the port.
The microsurgical instrument may comprise a vitrectomy probe, an aspiration probe, or other cutting probe. In the vitrectomy probe embodiment, the present invention yields the ability to adjust flow rate into the probe and aperture of the probe for a given cut rate so as to effectively perform a wide variety of vitreoretinal surgical objectives.